I recently interviewed four Republican Senate candidates in the space of one week, and if I had to draw a single assessment from those meetings it would be that there is plenty of diversity in the GOP’s class of Senate hopefuls.The four differed in stature, style and background, and they dealt with the party’s internal debate of style and strategies in a variety of ways.

Republicans must hold South Carolina and win at least one — maybe more — of the other three races to have any chance of taking back the Senate next year. And that makes these contests in South Carolina, North Carolina, Iowa and Alaska all worth watching.

On one end of the continuum was state Sen. Lee Bright, one of three conservatives who hopes to deny South Carolina Sen. Lindsey Graham renomination and win the GOP nod himself.

Bright, whose professional career started with selling televisions at Circuit City, has experienced a series of business setbacks. In fact, I’m not entirely clear how he makes a living, though he said something about truck brokerage and credit card processing. He seems affable, but he lacks gravitas.

The state senator describes himself as a member of the tea party and he endorsed first Michele Bachmann, then Ron Paul in the race for the Republican presidential nomination in 2012. He readily acknowledges that he rarely supports bills brought up for a vote on the floor of the South Carolina Senate.

Tillis, who grew up in a working-class family and didn’t earn a college degree until he was 37 years old, became a management consultant. He eventually became a partner with PricewaterhouseCoopers before moving to IBM.

He knocked off an incumbent Republican legislator in 2006 and ran for speaker four years later, defeating the party’s minority leader, who sought to move up the ladder.

Tillis checks all of the conservative boxes on his website. He is anti-abortion, believes “marriage is between one man and one woman,” says that “ObamaCare is a cancer on our national economy,” opposes amnesty for illegal immigrants and thinks Congress should “solve our border security crisis ... before it even debates any other changes to our immigration laws.”

But Tillis has taken some criticism from the most conservative elements of his party for being willing to negotiate with opponents and for evaluating legislation with an eye to eventual passage. He did not pander to his party's libertarian or tea party wings during my meeting with him, and he has the style that many successful Senate candidates possess. If nominated, he should be a formidable general-election candidate.

Iowa Republican David Young knows plenty about being a senator, though his knowledge comes from years as a Senate staffer. He served as chief of staff to Kentucky Sen. Jim Bunning and later moved to the same position in the office of Iowa Sen. Charles E. Grassley. Young grew up in Van Meter, Iowa, the hometown of Hall of Fame pitcher Bob Feller.

The former staffer faces two other formidable GOP opponents — a sitting state senator and a former U.S. attorney — in the race for the Republican Senate nomination. He argues that he has seen big government up close and knows what needs to be done to restrain it.

But while Young may know what buttons to push, it’s unclear whether the most conservative elements of the party will find him bombastic enough. The winner of the Republican nomination will face Democratic Rep. Bruce Braley, who hopes to hold retiring Sen. Tom Harkin’s seat for the Democrats.

Of the four, Treadwell was the most difficult to figure out, possibly because he spent so much of his time complaining about an article that my colleague, Nathan Gonzales, had written for my newsletter. No matter what question we asked, Treadwell somehow brought it back to what he regarded as an oversight or mistake in the article. He was clearly peeved, and that made him less affable and likable.

Treadwell attended Sandy Hook Elementary School in Newtown, Conn., where his father once served as first selectman. He stressed his conservatism and emphasized repeatedly that he has good support within the tea party community.

But it isn’t entirely easy to see this Connecticut-born Republican, who attended prep school at Hotchkiss and earned an undergraduate degree from Yale and an MBA from Harvard Business School, as an anti-establishment tea party guy. Treadwell worked extensively with former GOP Alaska Gov. Walter Hickel, who earned a reputation as a moderate when he served as secretary of the Interior.

Given Joe Miller’s defeat of Lisa Murkowski in the state’s 2010 GOP primary, Treadwell certainly must be concerned about his right flank. He clearly believes that it’s now his turn to take on incumbent Democrat Mark Begich, and the lieutenant governor obviously is not happy that Daniel S. Sullivan (Harvard, Georgetown Law School), the commissioner of the Alaska Department of Natural Resources, has jumped into the contest.